Process for making tetramethyl lead



United States Patent 3,426,056 PROCESS FOR MAKING TETRAMETI-IYL LEAD Charles Anthony Sandy, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington,

Del., a corporation of Delaware No Drawing. Filed Feb. 24, 1965, Ser. No. 435,043 U.S. Cl. 260-437 Claims Int. Cl. (307E 7/26 ABSTRACT OF THE DISCLOSURE Method of preparing tetramethyl lead by reaction of methyl chloride and monosodium lead alloy in the presence of a caboxamide catalyst of the formula RCONR R wherein (l) R, R and R separately are H or C -C alkyl and total up to 3 carbon atoms when said R and R are alkyl, and

(2) R and R together constitute a C -C polymethylene radical, when R is H or methyl.

Optionally, water or a C -C aliphatic hydrocarbon alcohol may be used as a catalyst promoter.

The present invention is directed to a novel process for producing (TML) tetramethyl lead from (MeCl) methyl chloride and monosodium lead alloy (NaPb) in the presence of a carboxamide as catalyst and combination thereof with hydroxylic compound as catalyst promoter.

Tetramethyl lead is now in demand as an anti-knock. Its manufacture, however, poses difiiculties, as discussed by Jarvie et al. in U.S. Patent 3,048,610; Tullio in U.S. Patent 3,072,694 and U.S. Patent 3,072,695; and Cook et al. in U.S. Patent 3,049,558. It appears from this art that the methyl chloride-monosodium lead alloy system is unique in that only certain metal compounds are effective to promote formation of TML. Such catalysts, however, including the aluminum compounds now used commercially, are not entirely satisfactory. In direct contrast to the well known ethyl chloride-sodium lead alloy system, which does not require catalysis below 100 C. but can be accelerated by ketones, alcohols, esters and other substances known to the art as ethylation accelerators, the methyl chloride-sodium lead alloy system responds not at all to conditions normally conducive to the formation of tetraethyl lead. In fact, from the disclosures of the recent practitioners of the art, it appears that the methylation of sodium lead alloy is unique in that only certain catalysts of the aluminum type have been found to be effective. Such high degree of catalyst specificity appears characteristic also of the mixed methylation-ethylatlon of sodium lead alloys as disclosed by Calingaert et al in U.S. Patent 2,270,109. The alkyl aluminum derivatives they form in the reaction mass are sensitive to the air and moisture and tend to ignite spontaneously on exposure to the atmosphere. Also the reaction masses are sticky and troublesome to discharge from the reactor.

It is, therefore, an object of this invention to provide a technically significant and novel process for producing tetramethyl lead, which process does not involve the use of aluminum compounds in addition to avoiding the hazards and process difiiculties attending use of prior methylation catalysts.

These and other objects of the invention will become apparent from the following description and claims.

Midgley, U.S. Patent 1,622,228 discloses reaction of alkyl halides broadly with active lead compounds, including sodium lead alloys broadly, in the presence of Water or other source of nascent hydrogen plus a cat- 3,426,056 Patented Feb. 4, 1969 alyst which may be acetamide among other compounds such as NH amines in general, and quaternary ammoniums.

Clem, U.S. Patent 2,464,399 shows carboxamides accelerate the EtCl-NaPb reaction; however, there is no reference to MeCl and no disclosure that other reagents can be used with the amide for advantageous effects.

More specifically, the present invention is directed to a novel process for making TML by reacting NaPb with a methylating agent which consists essentially of MeCl in the liquid phase at 25-120 C. in the presence of a catalytically effective amount of a carboxamide,

RCONR R wherein 1) R, R and R separately are selected from the group consisting of H and C -C, alkyl (preferably nalkyl), and total up to 3 carbon atoms when said R and R are alkyl; and

(2) R and R together constitute a C -C polymethylene radical (forming with --CONR a cyclic amide) and R is H or methyl; and, optionally but preferably, said carboxamide in combination with up to about 0.1 mole/mole NaPb of water or a C C aliphatic hydrocarbon alcohol.

Preferred embodiments include those wherein:

(a) reaction is effected with 1-6 moles of MeCl, 0.025-

0.5 mole carboxamide, and 0.001-0.01 mole hydroxylic compound per mole NaPb, at a temperature of at least C.;

(b) the hydroxyl/ amide ratio is 1/100-1/2;

(c) the amide is an acetamide or a propionamide, particularly N,N-dimethylacetamide or propionamide; (d) the hydroxyl compound is water or methanol; and (e) the water is introduced with the MeCl in concentrations of from to 3000 ppm, most preferably 200- 500 ppm, based on the MeCl.

The heretofore defined amides show moderate activity alone, and are most efiective at the elevated temperatures (e.g. 100 C.). Their use alone is believed unobvious in view of the prior methylation art which teaches that aluminum (and certain other metal) compounds are required and that the usual ethylation accelerators are ineffective.

The amides and hydroxyl compounds :as herein utilized interact synergistically to unexpectedly provide markedly improved TML yields.

Representative carboxamides include formamide, acetamide, propionamide, butyramide, valeramide (primary amides); N-methyl formamide, N-methyl acetamide, N- methyl propionamide, and the corresponding N-ethyl, N-propyl and N-butyl compounds (secondary amides); N,N-dimethyl formamide and N,N-dimethyl acetamide (tertiary amides); 'y-butyrolactam (2-pyrrolidone), ecaprolactam, and the corresponding N-methyl lactams (cyclic secondary and tertiary amides).

The aliphatic hydrocarbon alcohol which is optionally utilized in the practice of the herein described and claimed process may be saturated or unsaturated.

Representative compounds are the simple alkanols and cycloalkanols such as methanol, ethanol, 1- and 2- propanol, l-butanol, 2-methy1-2-propanol, pentanol, hexanol, 3,5,5-trimethylhexanol, cyclopentanol, and cyclohexa- The term methyl halide methylating agent consisting essentially of methyl chloride includes methyl chloride as the essential source of methyl groups and mixtures thereof with up to about 5 mole percent methyl iodide or more usually less than about 1 mole percent of the iodide. Such small proportions of iodide, e.g. 0.1-1 mole percent tend to promote the amide-catalyzed reaction, resulting in higher yields in a shorter time.

The MeCl may contain rather large porportions of water as given in the defined preferred embodiments. Thus, in contrast to prior practice regarding the alkylation of monosodium lead alloy, it is not critical for practical operation to exclude or limit moisture to very low levels. MeCl containing 50 p.p.m. or less of H is generally considered in this art to be substantially anhydrous. For example, in aluminum-catalyzed methylation, it is considered desirable to limit the water content of the MeCl to less than 150 p.p.m. and in general to operate as anhydrously as possible, both costly expedients.

Monosodium lead alloy, i.e. containing 50 mole percent Na and 50 mole percent Pb, or on a weight basis 10% wt. Na and 90% wt. Pb, has been amply described in the art. It may be used in various forms, usually comminuted, including ground as in Stecher US. Patent 2,135,091, flaked as in Pyk U.S. Patent 2,561,636 or Tanner US. Patent 2,635,107 and quenched (in MeCl) as described by Mattison in US. Patent 2,744,126.

The over-all process of this invention comprises (1) mixing the alloy, methyl halide, carboxamide, and the water or other hydroxylic component,

(2) holding such mixture at a temperature in the range of 25 to 120 C. at which reaction begins and proceeds at a reasonable rate, and

(3) recovering the TML from the reaction mass. Normally the reaction is agitated, usually in the presence of an inert solid such as graphite as an internal lubricant. From about l5% by weight of the alloy may be used, depending on the dimensions of the reactor, the effective ness of the agitation means, and the proportions of the reactants, There may also be present a thermal stabilizer for tetramethyl lead, as described by Jarvie et al. in U.S. Patent 3,048,610 and Cook et al. in U.S Patent 3,049,558, for example a volatile hydrocarbon such as toluene or isooctane having boiling characteristics comparable to those of tetramethyl lead.

The reactants, catalyst components and other agents as described above may be introduced separately or together, all at once or gradually during the course of the reaction. The catalyst components may be added as such or in a carrier which conveniently may be the methylating agent or an inert solvent including the thermal stabilizers toluene and isooctane.

The reaction mass components may be mixed at temperatures at which the reaction does not proceed at a substantial rate, e.g. below 25 C., and the mixture then brought to operating temperatures. Or the reactants and other essential components may be brought into contact at temperatures within the operating range. The reaction may be conducted batchwise or continuously.

Reaction mass temperatures are readily controlled by controlling the amount and schedule of catalyst and methyl chloride addition, by cooling where necessary and by refluxing methyl chloride. The internal pressure should be sutficient to maintain methyl chloride in liquid phase.

The resulting reaction mass may be worked up in the usual ways described in the art. Normally the residual methyl chloride is vented from the charge at a temperature in the range of about 25 to about 60 C. and is passed to a recovery system as in tetraethyl lead technology. For this purpose the reaction mass temperature is adjusted accordingly. The tetramethyl lead is then recovered by solvent extraction, e.g. with toluene or by steam distillation according to the well known techniques.

In the representative examples which follow: parts means parts by weight; Y=percent yield of TML based on the quantity of alloy employed; C=percent of alloy consumed in the formation of all products, including byproducts as well as TML; and Y/C=a measure of the specificity of the reaction to produce TML at the expense of side products.

EXAMPLE I Illustrated here is the eflect of water on the amidecatalyzed reaction. In the general procedure a steel bomb was charged with (a) parts crushed 10 on 20 mesh NaPb enclosed in a glass ampoule and (b) carboxamide as described below. Then, with the bomb cooled to 70 C., the bomb atmosphere was replaced by dry nitrogen and 130 parts MeCl Were admitted from a pressurized source, corresponding to a loading density of 0.52 gram MeCl/cc. of bomb capacity. At about 0 C. the closed bomb was struck sharply against a solid object to break the ampoule, placed in a preheated oil bath and its contents vigorously agitated by shaking. Reaction was terminated by cooling to -70 C. and the tetramethyl lead recovered by extracting the reaction mass with toluene.

(A) Table 1A reports results obtained in a. series of early runs before the water-effect was recognized. The H O content of the MeCl lots was later determined to be 4060 p.p.m. No attempts had been made to rigorously exclude moisture from the system, as by baking the equipment. It is assumed the MeCl was the main source of H 0.

TABLE IA.CARBOXAMIDE-CATALYZED METHYLATION Molar MeC1/Nalb=5.92 40-60 p.p.m. H2O in the MeCl Molar HzO/NaPb=0.00067-0.001 Reaction temp.= 0., time=l.5 hrs;

Carboxaruide Molar HzO/Amide TML Amide/NaPb Y Formamide 0. 143 1/143 41 N,N-dimethyl tormamide. 0. 148 1/148 44 Acetamide 0. 1/125 55 N,N-dimethyl acetamide- 0. 1/185 59 N-methyl caprolactam 0.114 1/114 52 N -methyl-2-pyrrolidone 0.110 1/110 45 The HzO/amide ratio is based on 0.001 HzO/NaPb.

Molar MeCllNaPb=5.92

9 p.p.m. H2O in the MeCl Molar HgO/NaPb as noted below Molar amide[NaPb=0.125

Reaction temp.=l10 0., time=1.5 hrs;

Additional Hi0 Total Molar HzO/Amide TML HzO/NaPb Y None 0. 00015 1/833 7 0.5 Part 0. 064 1/2 71 Corresponds to 3,840 p.p.m. based on the MeCl.

When the above procedures are repeated with MeCl containing 25 p.p.m. H O but in the absence of the carboxamide, the TML yield is nil.

EXAMPLE II The hydroxyl effect is further illustrated.

(A) The data in Table II below were obtained according to the following procedure, involving a stainless steel pressure reactor equipped with outer electrical heating means and inner thermocouples for measuring temperature and adapted for agitation by shaking. The reactor volume is such that 100 parts MeCl corresponds to a loading density of 0.25 gr./ cc.

100 parts 10 on 20 mesh NaPb and 2.7 parts DMAC were added under nitrogen. The reactor was closed, cooled to 70 C. and evacuated, and 69 parts methyl chloride containing known quantities of H 0 were added.

Agitation was started and the reaction mixture brought to 110 C. in 5 to minutes and held there for 2 hours. Reaction was terminated by cooling to -70 C. Tetramethyl lead was recovered by extracting the reaction product with toluene.

TABLE II.-WATER EFFECT IN DMAC-CATALYZED METHYLATION Molar MeOl/NaPb=3.14

H2O in MeOl as noted below Molar HzO/NEP'D as noted below Molar DMAC/NaPb=0.071

Molar LEO/DMAC as noted below 2 hours reaction at 110C.

(B) The above procedure was repeated except that 0.16 part of methanol was added to the system to provide 0.012 mole hydroxylic compound per mole NaPb, which corresponds also to 1 mole CH CH/ 6 moles DMAC. Water introduced with the MeCl (50 ppm. corresponding to 0.00044 mole/mole NaPb) was negligible in comparison.

The TML yield was 83%. In contrast, in absence of the alcohol, the yield was only 5% (Table II).

(C) The Example II-A procedure was repeated except that no amide was added and the methyl chloride contained 387 ppm. H O corresponding to a molar H O/NaPb ratio of .0034. The TML yield was .4, the alloy conversion 1.2 and Y/ C .33.

EXAMPLE HI Illustrates effect of carboxamide structure on activity as catalyst (Tables III A, B and C). The general procedure described in Example I was employed with reaction conditions I or II as follows:

TABLE IIIA.-EFFECT OF STRUC- TURE ON CARBOXAMIDE ACTIVITY IN METHYLATION Primary Arnides Conditions TBS/{IL H'CONHZ II 36 Me-CONHz. I 29 Et-CONHz--. I 53 Et-C ON H2. *II 67 ll 50.063 mole amide/mole NaPb; HzOIamide= TABLE 11113 Conditions Tl l dL Seoonnary Amides H-OONH-Et. Me- Et-CONH N ma i- TABLE IIIC Tertiary Amides Conditions TBS/ IL The eifect of procedure I or II appears minor compared to the efiect of amide structure. Example III (above) and Example IV (below) indicate, however, the higher the temperature, the better the yield.

EXAMPLE IV Example III was repeated under reaction conditions II with propionamide as catalyst (0.16 mole/mole NaPb) at a reaction temperature of 25 C. for one hour. The yield of TML was 24%.

EXAMPLE V Reaction-promoting effect of Mel Example I was repeated under the conditions described in Table IA. The DMAC concentration (4.75 parts) corresponds to 0.125 mole/mole NaPb. In a first run, with MeCl as the sole alkylating agent, the TML yield was 57%, Y/C 0.81. In a second run, there was added 0.1 mole percent MeI, based on the MeCl; the TML yield was 77% with Y/C 0.81.

EXAMPLE VI The Example I procedure was repeated with and without added alcohol as catalyst promoter. The conditions and results are tabulated below:

TABLE IV.HIGHER ALCOHOL PROMOTED CARBOX- AMIDE CATALYZED METHYLAIION Molar MeOl/NaPb=5.92

24 ppm. H2O in the MeOl Molar HzO/NaPb .00022 Molar alcohol/NaPb=.005

Reaction temp.= 0., time=1.5 hrs. Carboxamide=N,N-dimethylacetamide Molar amide/NaPb .132

Alcohol Present Y C Y/O N0 6. 1 l7. 1 354. Yes c- 68. 4 80. l 854 The Example I procedure was repeated with N-tertiary butyl formarnide as catalyst at a molar amide/NaPb ratio: .1 15.

The other conditions were:

Molar MeCl/NaPb=5 .92

500 -p.p.m. H O in the MeCl Molar H O/NaPb=0.0082

Reaction temp.=1l0 C., time=1.5 hrs.

The yield was 14.6%.

The preceding representative examples may be varied Within the scope of the present total specification disclosure, as understood and practiced by one skilled in the art, to achieve essentially the same results.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are as follows:

1. A process for making tetramethyl lead which comprises reacting monosodium lead alloy with at least about 1 mole, per mole of said alloy, of a methyl halide methylating agent consisting essentially of methyl chloride in the liquid phase at a temperature within the range of 25 to C. in the presence of a catalytically efiective amount of a combination catalyst consisting essentially of (A) carboxamide of the formula RCONR R wherein (1) R, R and R separately are selected from the group consisting of H and C -C alkyl and total up to 3 carbon atoms when said R and R are alkyl, and

7 (2) R and R together constitute a C -C polymethylene radical when R is selected from the group consisting of H and methyl; and (B) from about 0.001 to about 0.1 mole, per mole of said monosodium lead alloy, of a hydroxylic compound selected from the group consisting of water and a C -C aliphatic hydrocarbon alcohol.

2. The process of claim 1 in which R, R and R separately are selected from the group consisting of H and C C alkyl and total up to 3 carbon atoms when said R and R are alkyl.

3. The process of claim 1 in which R and R together constitute a C C polymethylene radical when R is selected from the group consisting of H and methyl.

4. The process of claim 1 wherein said reaction is effected with, from 1 to 6 moles of methyl chloride, from 0.025 to 0.5 mole of said carboxamide and from 0.001 to 0.01 mole of said hydroxylic compound per mole of said alloy, at a temperature of at least 80 C.

5. The process of claim 4 wherein said carboxamide is N,N-dimethylacetamide and the hydroxylic compound is methanol.

References Cited UNITED STATES PATENTS Midgley 260-437 Monroe et a1 260-437 Calingaert et al. 260-437 Clem 260-437 Tanner 260-437 Jarvie et a1 260-437 Tullio 260-437 Tullio 260-437 Sandy 260-437 Scales 260-437 Kobetz 260-437 Beaird et a1. 260-437 Beaird et a1 260-437 Kobetz 260-437 Beaird et a1 260-437 Pedrotti et a1 260-437 TOBIAS E. LEVOW, Primary Examiner.

H. M. S. SNEED, Assistant Examiner. 

